This invention relates to decoding spatiochromatically multiplexed digitized color images with applications to compression, transmission, reception, storage, and improving image quality.
Related background material and disclosure are found in coinvented and coassigned U.S. Pat. No. 5,398,066, (the '066 patent) and coinvented and coassigned U.S. application Ser. No. 08/401,825, filed Mar. 10, 1995, U.S. Pat. No. 5,541,653, both incorporated herein by reference for all purposes. Other background information and descriptions of the prior art may be found in the references cited and submitted along with those applications.
As the above referenced documents thoroughly describe, in digital image processing, a representation of an image is typically stored and transmitted as an array of numerical values. The image is divided up into a grid. Each small square in the grid is referred to as a pixel. The intensity of the image at each pixel is translated into a numerical value which is stored in an array. The array of numerical values representing an image is referred to as an image plane.
Black and white (gray scale) images are commonly represented as a two-dimensional array where the location of a pixel value in the array corresponds to the location of the pixel in the image. Each location in the array for gray scale images can commonly store a number, for example, an integer value of between 0 and 255 (an 8-bit binary number). This means that there can be 1 of 256 different gray levels displayed at each pixel in the image.
Color images are commonly represented by three two-dimensional arrays. Each array (or plane) represents one of the primary colors, e.g., red, green, or blue. The planes overlap so that each pixel in the displayed image displays a composite of a red, green, and blue value at that pixel. In a common 24-bit color system, each pixel in each of the three planes can store a value of between 0 and 255. This means that there can be 1 of 256.sup.3 or 16 million different colors displayed at each pixel. Typical digital color images can range in size from 10.sup.7 bits/image (a TV frame) to 10.sup.10 bits/image (a satellite image) thus posing problems for efficient storage and transmission.
In practice the number of bits required to represent the information in realistic digital images may be greatly reduced without significant loss in perceived quality by taking advantage of the fact that in ordinary images the pixel values tend to be strongly redundant in three domains: spectral (because pixel values from different spectral bands-e.g., RGB-are generally highly correlated); spatial (because neighboring pixels also tend to be highly correlated); and, for dynamic images, temporal (because consecutive frames tend to be very similar). Image compression techniques can reduce the number of bits required to represent images by removing these redundancies.
The above cited references discuss one type of prior art digital color image system having a single array CCD-type cameras with a mosaic color filter covering the CCD array. These cameras, by their inherent nature, produce a representation of an image that contains just one color component at every pixel. The arrangement of the components is determined by the mosaic pattern in the filter. Digital images produced by such systems are referred to as being spatiochromatically multiplexed.
The above cited references also discuss two other means of producing a spatiochromatically multiplexed digital image plane, (hereinafter referred to as an M plane) either by decoding a 3-plane image as described in the '066 patent or by using a multiple array CCD-type cameras with array offset and interpreting the multiple array CCD image as a single spatiochromatically multiplexed plane and then decoding that plane to produce a resolution enhanced image as described in the '825 application.
However the M plane is produced, and whatever the pattern of spectral pixels in the M plane, the M plane must generally be decoded before viewing to recreate full multi-spectral image planes. Prior art methods for decoding spatiochromatically multiplexed digital images have commonly required that the image first be decoded as a YIQ JPEG image before being reconstructed as a full three-plane RGB image, as discussed in previously cited references.
The inventors of the present invention described in the '066 patent a method and system for decoding spatiochromatically images directly, without conversion to another color representation such as YIQ. This decoding has proven and been described as useful for any spatiochromatically multiplexed plane, regardless of how produced, including multiplexed planes using just two spectral components.
While this has been shown to be a simplification and improvement over systems that require YIQ conversion, even in this decoding, a multi-pass mathematically process is required to decode high-quality images. This process can be complex to implement and can consume a large amount of computer resources.
What is need is a method and system capable of more quickly and efficiently decoding a spatiochromatically multiplexed image plane to derive a full multi-spectral image. Preferably, the method will be generalizable to advantageously decode a number of different types of spatiochromatically multiplexed planes while requiring a minimum of calculations and processing.